1. Field of the Invention
The present invention relates to a variable attenuator for use in optical fiber communication and optical network technology, and particularly to a variable attenuator with stopper mechanism.
2. Description of Related Art
An optic attenuator is a passive optical component for reducing optical power propagating in an optic fiber, and may perform fixed or variable attenuation. Optical attenuators are widely used in optical transmission systems and optical networks.
A general variable attenuator has a filter. The filter has an effective filter region disposed in the optical path between a collimator and a reflector. The filter has a filter density which varies from a low density region to a high density region. The transmitted light is attenuated to different intensities by linear movement of the filter with respect to the optical path of the light.
For example, U.S. Pat. No. 4,702,549 describes a variable optical attenuator comprising two optical fibers having their ends aligned to and opposite to each other and a filter element mounted on a reciprocating means for being selectively positioned between the fiber ends. The filter is not perpendicular to the axis of alignment of the fiber ends. The variable attenuator has a manually-operated screw rod to control the attenuation of the transmitted light. A disadvantage associated with such as conventional design is that no stopper is employed to stop the operation of the device whenever needed. Controlling the angular position of the screw rod while rotating the screw rod near the highest and lowest attenuation positions is difficult. The screw rod can be easily over-rotates at positions near the highest and lowest attenuation. Devices of U.S. Pat. No. 4,989,938 and U.S. Pat. No. 4,904,044 share the same problem.
U.S. Pat. Nos. 6,144,794 and 6,130,984 each describe a variable attenuator using reciprocating means to adjust the position of the filter in the variable attenuator. Both employ an electrical control system. Although electrical control systems operate with higher precision, their cost is high and they greatly increase the size of the device.
The present invention provides a variable attenuator incorporating a stopper structure in a reciprocating means for preventing over-movement of the attenuation filter beyond the highest and the lowest attenuation positions.
An object of the present invention is to provide an improved variable attenuator having a stopper mechanism. The stopper mechanism prevents the filter from moving beyond its end-point positions.
A variable optical attenuator of the present invention comprises a cover, a housing an optical module and a reciprocating means.
The housing has a hollowed-out interior with an inner cavity in a lower end of the housing. A pair of locating slots define lateral sides of the inner cavity. An inner sidewall defines a forward boundary of the inner cavity. A side hole communicates between one of the locating slots and an outside wall of the housing. A fixing groove and a supporting portion are formed adjacent the other locating slot.
The optical module comprises a frame, a reflector and a collimator. The frame has a groove with an inner wall, and a through hole communicating with the groove. The reflector is fixed on the inner wall of the frame and is disposed coaxially with the through hole. The collimator is positioned in the through hole and fixes ends of an input optical fiber for carrying the transmission optical signals to the attenuator, an output optical fiber for receiving the resulting attenuated transmission optical signals from the attenuator.
The reciprocating means comprises a carrier for carrying the filter, a spring element, and a screw rod. A pair of stoppers is formed at two opposite sidewalls of the carrier. A fixing groove is formed at one of the other two opposite sidewalls. The spring element has a fixing portion and a mating portion. The screw rod has a screw portion at its middle and a holding portion at each end.
When assembled, the carrier moves lengthwise along the screw rod when the screw rod is rotated. The filter is fixed onto the carrier and moves along with the carrier. The fixing portion of the spring element is inserted into the fixing groove. The mating portion of the spring element abuts against the inner sidewall and moves along the inner sidewall when the carrier is moved.
By rotating the screw rod first in one direction and then in the reverse direction, the carrier with the filter can be made to move first toward one side and then toward another side of the housing. The direction of movement of the filter is perpendicular to the path of the input and output light. The filter has a filter density which varies between a lower density region and a higher density region along a linear filter axis. When the carrier arrives at one end of the screw rod, the stoppers abut with surfaces of the corresponding locating slot and the part of the filter penetrated by the input and output light will be either the lower density region or the higher density region.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.